Re: Best way to stop a crack
Burnman, try drilling a little farther away from the end of the crack, up to an eighth or quarter inch. This is a tricky deal because the crack can take a quick left hand turn and miss the bullseye altogether. If the crack is pointy on the end, it may extend farther than you think because the little tiny narrow end of the crack is tight and just sort of disappears, even though it still continues on. If it's square on the end, that may be the true end of the crack.
Don't drill all the way down to the PVB. The function of your drill hole is to be deep enough to allow you to make a bullseye that extends from the surface all the way down to the PVB and will intercept the crack. If you drill too deep, there is no glass left to make a bullseye. Or you might say that there is a tiny bullseye way down there at the bottom that has no chance of intercepting the crack. The crack just runs over the top of the bullseye shoulder. The drill hole should not go more than half way thru the outer layer and should never touch the PVB because it can be damaged. Also, if you hit the PVB with the bit, you will burn it and leave black residue in the hole.
As for bit size, the smaller the better, when it comes to a nice look. The downside is that little tiny skinny drill bits are really fragile. You certainly don't want to break one off in the hole! Another problem with a drill hole is its tendency to trap an air bubble at the bottom, under the pit filler resin. Use a needle to drag that bubble out before you cure your pit filler.
Finally, the shape of the probe used to make the bullseye is important. A needle-sharp point will make a star. While this is useful in certain circumstances, what you really want for this operation is a blunt tip so you get a bullseye. My probe is blunt on one end and sharp on the other end and I just reverse it when necessary.
In the end, lots of practice will make you good at this. Mistakes or accidents will begin to diminish over time. And you will soon begin to appreciate the unpredictability of glass.
Best regards,
Dave Beyerlein
Master Trainer, NGA Certified
Dave's Windshield Repair
Cedar Park TX
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